Ensure EC private keys retain leading zeros
RFC5915 requires the use of the I2OSP primitive as defined in RFC3447
for storing an EC Private Key. This converts the private key into an
OCTETSTRING and retains any leading zeros. This commit ensures that those
leading zeros are present if required.
Reviewed-by: Andy Polyakov <appro@openssl.org>
diff --git a/crypto/ec/ec_asn1.c b/crypto/ec/ec_asn1.c
index 9bba26e..97c5906 100644
--- a/crypto/ec/ec_asn1.c
+++ b/crypto/ec/ec_asn1.c
@@ -1110,7 +1110,7 @@
{
int ret = 0, ok = 0;
unsigned char *buffer = NULL;
- size_t buf_len = 0, tmp_len;
+ size_t buf_len = 0, tmp_len, bn_len;
EC_PRIVATEKEY *priv_key = NULL;
if (a == NULL || a->group == NULL || a->priv_key == NULL ||
@@ -1126,18 +1126,32 @@
priv_key->version = a->version;
- buf_len = (size_t)BN_num_bytes(a->priv_key);
+ bn_len = (size_t)BN_num_bytes(a->priv_key);
+
+ /* Octetstring may need leading zeros if BN is to short */
+
+ buf_len = (EC_GROUP_get_degree(a->group) + 7) / 8;
+
+ if (bn_len > buf_len) {
+ ECerr(EC_F_I2D_ECPRIVATEKEY, EC_R_BUFFER_TOO_SMALL);
+ goto err;
+ }
+
buffer = OPENSSL_malloc(buf_len);
if (buffer == NULL) {
ECerr(EC_F_I2D_ECPRIVATEKEY, ERR_R_MALLOC_FAILURE);
goto err;
}
- if (!BN_bn2bin(a->priv_key, buffer)) {
+ if (!BN_bn2bin(a->priv_key, buffer + buf_len - bn_len)) {
ECerr(EC_F_I2D_ECPRIVATEKEY, ERR_R_BN_LIB);
goto err;
}
+ if (buf_len - bn_len > 0) {
+ memset(buffer, 0, buf_len - bn_len);
+ }
+
if (!ASN1_OCTET_STRING_set(priv_key->privateKey, buffer, buf_len)) {
ECerr(EC_F_I2D_ECPRIVATEKEY, ERR_R_ASN1_LIB);
goto err;
